Battery separator

ABSTRACT

A battery separator for alkaline storage batteries of the nonwoven fiber mat type; the fiber mat being impregnated with a polymeric binder and a monomeric wetting agent, the thus impregnated mat being subjected to irradiation to form a crosslinked unitary structure.

United States Patent [72] Inventor 21 Appl. No. [22] Filed [45] Patented [73] Assignee [54] BATTERY SEPARATOR 4 Claims, No Drawings [52] U.S. Cl 136/146, 1 17/9331 [51] Int. CL. l-l01m 3/00 [50] Field of Search 136/146, 142,143, l48;117/93.31, 138.8 A; 260/2.1

[56] Reierences Cited UNITED STATES PATENTS 2,482,062 9/1949 Hanson 136/ 146 2,965,697 12/1960 Duddy 136/146 3,092,519 6/1963 Olson 136/146 3,10l,276 8/1963 Hendricks 117/56 3,111,424 11/1963 LeClair 117/93.31 X 3,186,876 6/1965 Piechon 136/143 3,188,165 6/1965 Magat et a1..... 117/93.31 X 3,216,864 11/1965 Bushrod et a1 136/148 3,240,723 3/ 1966 Friedlander 260/2.1 3,330,702 7/1967 Horowitz 136/146 3,427,206 2/1969 Scardaville et a1 136/ I 46 Primary Examiner-Winston A. Douglas Assistant Examiner-A. Skapars Attorney lrving Seidman ABSTRACT: A battery separator for alkaline storage batteries of the nonwoven fiber mat type; the fiber mat being impregnated with a polymeric binder and a monomeric wetting agent, the thus impregnated mat being subjected to irradiation to form a cross-linked unitary structure.

BATTERY SEPARATOR BACKGROUND OF THE INVENTION Storage batteries of the alkaline type, such as those utilizing a potassium hydroxide electrolyte, have their operational efficiency severely circumscribed by the nature of the separator elements used in the battery.

Various separator elements have been proposed including the fiber mat-type having various binder impregnants. It has been found that with known separator element s, high rate charging may be adversely affected; migratory phenomena within the cell may become excessive to thereby reduce the efficiency of the device, and other battery characteristics such as holding a charge, the discharge curve, etc., may be relatively poor.

Accordingly, an object of this invention is to provide an improved fiber mat battery separator which increases the efficiency of battery charge and discharge.

Another object of this invention is to provide an improved battery separator of the character described, wherein the fibers of the mat and impregnating agents for the mat are selected so that upon suitable irradiation of the impregnated mat, a cross-linking action takes place as between the several constituents of the mat, to produce a unitary structure having improved properties as they relate to usage in alkaline storage batteries.

Other objects of this invention will in part be obvious and in part hereinafter pointed out.

DESCRIPTION OF THE PREFERRED EMBODIMENT in accordance with the instant invention, a nonwoven fiber mat is formed from selected polymeric fibers of suitable denier and staple length; the mat then being impregnated with an aqueous solution of a polymeric unsaturated organic acid; the impregnated web being then hot calendared to a desired thickness and sprayed with a solution of a monomeric unsaturated organic acid-wetting agent. The thus impregnated web is subjected to selected conditions of irradiation to produce cross-linking effects and unitizing the web.

Thus, by way of illustration, a battery separator web of the instant invention was made as follows:

A nonwoven fiber web was formed on a Curlator Rando- Webber or other web forming equipment, utilizing polypropylene fibers of 3 denier, 1 9/16 inches staple length. The web is then saturated with an aqueous solution of polyacrylic acid, which is used in amounts to constitute 5 percent by weight of the completed article.

The saturated web is then calendared by a stand of heated calendar rolls to a thickness of about 8 mils. The material weight is about 2 ounces per square yard.

The calendared web is then sprayed with an aqueous solution of acrylic acid, in an amount such that the residual acid in the finished product amounts to about 5 percent by weight thereof.

The impregnated and coated web is then subjected to a 7 Mev linear accelerator to produce an irradition of about 2 megarads. The resultant product is then converted to battery separator elements in a manner known in the art.

It has been found that the use of battery separators of the instant invention, the efiiciency of alkaline-type storage batteries using potassium hydroxide electrolyte, as in a nickel-cadmium battery, is substantially improved and such battery is remarkably free of adverse migration phenomena and the like.

It is understood that in lieu of polypropylene fibers, polyethylene or polyamid fibers may be used. Also, the denier of the fibers may range from about 1.5 to about 15.

The web impregnant may be constituted of polymeric unsaturated organic acids such as polymethacrylic acid and polyitaconic acid in lieu of polyacrylic acid. The binder concentration may range from about 2 percent to about l5 percent based on the total weight of the finished product.

In place of the acrylic acid-wetting agent, other unsaturated organic acid monomers may be used, such as methacrylic acid and the like. The monomer can be combined with a trace amount (1 to 5 percent by weight) of a monofunctional monomer such as divinylbenzene to reduce the radiation dosage for the cross-linking action.

While the irradiation is preferably of the order of l to 2 megarads; the range may be from about 0.5 to 25 megarads.

lclaim:

1. A battery separator for alkaline storage batteries comprising a nonwoven, matted web of polymeric fibers selected from the group consisting of polypropylene, polyethylene and polyamide, a polymeric saturant distributed through said web, said saturant being selected from the group consisting of polyacrylic acid, polymethacrylic acid and polyitaconic acid, and a coating on said saturated web, said coating being selected from the group consisting of acrylic acid and methacrylic acid, said saturant and coating being irradiated in situ to provide a cross-linking of the fibers, saturant and coatmg.

2. A battery separator as in claim I wherein said fibers are of polypropylene having a 3 denier and a stable length of about 1.5 to about 2.0 inches.

3. A battery separator as in claim I wherein said fibers have a denier of from about 1.5 to about 10.0.

4. A battery separator as in claim 1, wherein said saturant amounts to about 5 percent by weight of the irradiated web. 

2. A battery separator as in claim 1 wherein said fibers are of polypropylene having a 3 denier and a stable length of about 1.5 to about 2.0 inches.
 3. A battery separator as in claim 1 wherein said fibers have a denier of from about 1.5 to about 10.0.
 4. A battery separator as in claim 1, wherein said saturant amounts to about 5 percent by weight of the irradiated web. 